Computing N -subjettiness for boosted jets

Abstract

Jet substructure tools have proven useful in a number of high-energy particle-physics studies. A particular case is the discrimination, or tagging, between a boosted jet originated from an electroweak boson (signal), and a standard QCD parton (background). A common way to achieve this is to cut on a measure of the radiation inside the jet, i.e. a jet shape. Over the last few years, analytic calculations of jet substructure have allowed for a deeper understanding of these tools and for the development of more efficient ones. However, analytic calculations are often limited to the region where the jet shape is small. In this paper we introduce a new approach in perturbative QCD to compute jet shapes for a generic boosted jets, waiving the above limitation. We focus on an example common in the substructure literature: the jet mass distribution after a cut on the N -subjettiness τ 21 ratio, extending previous works to the region relevant for phenomenology. We compare our analytic predictions to Monte Carlo simulations for both plain and SoftDrop-groomed jets. We use our results to construct analytically a decorrelated tagger.

The soft drop groomed jet radius at NLL

“…In this work, we focus on the soft drop grooming algorithm of [4]. Both on the experimental [5][6][7][8] and the theoretical side [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], significant progress has been made recently in improving our understanding of soft drop groomed jet observables. In the heavy-ion community, soft drop groomed jet substructure observables have also received increasing attention from both experiment [25][26][27][28] and theory [29][30][31][32][33][34][35][36][37][38][39].…”

New insights on an old problem: resummation of the D-parameter

“…When D ∼ C 2 , emissions that set the D-parameter therefore also set the event plane, and this backreaction is responsible for the D-parameter to lose additivity and prohibit any standard factorization. Related issues with factorization breakdown in endpoint regions of phase space have also been observed in studies of observables sensitive to multi-prong jet substructure [39,44,60]. Nevertheless, this does not imply that factorization is impossible.…”

Towards machine learning analytics for jet substructure

“…N -subjettiness distributions can be meaningfully calculated in perturbative QCD. These distributions have been the subject of several theoretical investigations [29,30,53] (see also [34,54,55] for theoretical studies on the related observable D 2 ). The N -subjettiness distributions were calculated explicitly at LL accuracy, i.e.…”